Cellular source in ewes of prostaglandin-endoperoxide synthase-2 in uterine arteries following stimulation with lipopolysaccharide

Prostaglandin-endoperoxide synthase (PTGS) (also known as cyclooxygenase) c onverts arachidonic acid into several prostaglandins, many of which have ro les in vasodilation and vasoconstriction under normal and pathological cond itions. There are two isoforms of PTGS: PTGS-1 and PTGS-2; PTGS-1 is consti tutively expressed in many tissues and is believed to be involved in the ho meostatic maintenance of the body, In contrast, PTGS-2 is believed to have a "differentiative" role in the cells and is highly inducible during inflam mation and in response to lipopolysaccharide (LPS). Endothelial cells as we ll as vascular smooth muscle cells can be a source of PTGS within the arter y. The objective of this study was to determine the cell population(s) in u terine arteries that respond to LPS with an increase in PTGS-2 protein expr ession. Uterine arteries collected from ewes during the follicular (Day 0, Day 0 = estrus, n = 4) or luteal (Day 10, n = 4) phase were treated in vitr o with LPS as intact artery segments, cut-open artery segments, or cut-open and denuded (endothelial cells absent) artery segments. After 24 h of LPS treatment, intact, cut-open, and denuded uterine artery segments were colle cted into homogenization buffer for determination of PTGS-2 protein levels by Western blot analysis. The culture medium was collected and used for det ection of 6-keto-prostaglandin F-1 alpha (6-keto-PGF(1 alpha)), the stable metabolite of prostacyclin, using an enzyme immunoassay. In addition, the l ocation of PTGS-2 after LPS treatment was analyzed by immunohistochemistry in intact artery segments. Denuded arteries (endothelium absent) did not sh ow increases in PTGS-2 protein in the homogenates or 6-keto-PGF(1 alpha) in the culture medium after LPS exposure. In contrast, cut uterine arteries r esponded to LPS stimulation with a significant increase in PTGS-2 protein i n homogenates and 6-keto-PGF(1 alpha) in culture medium. Immunohistochemica l staining for PTGS-2 was associated with both endothelial cells and vascul ar smooth muscle cells. These results suggest that while both endothelial c ells and vascular smooth muscle cells are associated with PTGS-2, after LPS exposure it is the endothelial cells that are essential in uterine artery increases in PTGS-2 and prostacyclin in response to LPS stimulation.